The disclosure relates to abradable coatings. More particularly, the disclosure relates to cold section abradable coatings for gas turbine engines.
Abradable rub materials are used in all stages of gas turbine engines (broadly inclusive of aero engines, industrial gas turbines, and the like). They may line the inner diameter (ID) surfaces of case segments, blade outer air seals (BOAS), or similar components facing airfoil tips.
A wide variety of rub materials are used, varying largely with the position in the engine. Position is highly correlated with temperature, with temperature generally increasing downstream through the fan (if any) and compressor stages and spiking in the combustor and then decreasing through the turbine stages. The “cold section” of the engine is generally identified as being upstream of the combustor. In lower temperature (upstream) regions of the cold section, one family of aluminum-based coatings has an Al—Si matrix. METCO 601NS (trademark of Oerlikon Metco, Winterthur, Switzerland) is a known example having 7 weight percent Si, 40 weight percent polyester, remainder Al. These may be a blended powder applied by atmospheric plasma spray. The polyester (or other polymer) acts as a fugitive which burns or volatizes off in a post-application heat treatment or in engine operation. Variants have been proposed including additional non-metallic fillers such as solid lubricants (e.g., hexagonal boron nitride (hBN)).
In cold section applications, such material typically interfaces with titanium alloy blades (e.g., Ti6Al4V).
Separately, United States Patent Application Publication 20160168663 A1, of Thomas J. Watson et al., Jun. 16, 2016 and entitled “Aluminum Alloys and Manufacture Methods”, hereinafter the '663 publication, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length, discloses I-phase aluminum alloys used, e.g., in blades.